Hey I wanted to know the cheapest place to find these things. Im looking for one with a lock on it.

I searched ebay but came up with one but not sure if it will fit my 2006 Mark LT. Craigslist around me is trash. No one has anything. I dont trust doing business on craigslist outside my area.

 

Here's what i found in my search after i got my truck...I don't know about locking, but there are some nice looking ones here and it is a start.
http://www.solidbydesign.com/sbd/FuelDoors.aspx